Patterns of cell proliferation and apoptosis by topographic region in normal Bos taurus vs. Bos indicus crossbreeds bovine placentae during pregnancy

In this study, the proliferation activity and apoptosis in different regions of normal bovine placenta (central and boundary regions of placentomes, placentomal fusion, microplacentomes, and interplacentomal regions), from distinct gestation periods (Days 70 to 290 of pregnancy), were analyzed by flow cytometry.Our results indicated that microplacentomes presented a lower number of apoptotic cells throughout pregnancy, with a higher proliferative activity by the end of gestation, suggesting that such structures do not contribute significantly to normal of placental functions and conceptus development during pregnancy. The placentome edges revealed a higher number of apoptotic cells from Day 170 on, which suggests that placentome detachment may well initiate in this region.Variations involving proliferation and apoptotic rates may influence placental maturation and detachment, compromising placental functions and leading to fetal stress, abnormalities in development and abortion, as frequently seen in bovine pregnancies from in vitro fertilization and cloning procedures. Our findings describing the pattern of cell proliferation and apoptosis in normal bovine pregnancies may be useful for unraveling some of the developmental deviations seen in nature and after in vitro embryo manipulations.In ruminants, the placenta is classified as cotyledonary on the basis of its gross anatomical features. The immediate feto-maternal contact in the bovine placenta is restricted to multiple discrete structures called placentomes, consisted of the maternal part, the caruncle, and the fetal part, the cotyledon. In early gestation, caruncles and cotyledons are not connected yet, without formation of placentomes [1-3]. Placentome formation can be considered a gradual process that takes place immediately after pregnancy recognition, being fairly completed by the end of organogenesis [4]. Once established, bovine placentomes grow continuously throughout pregnancy. However, placentome growt